Radar sensors are used, for example, in motor vehicles to detect the surroundings of the vehicle and to locate preceding vehicles. They may be used as independent distance warning systems or also may be part of a driver assistance system.
For reasons of space, weight, and cost, they are typically implemented in motor vehicles as integrated radar sensor components, so-called monolithic microwave integrated circuits (MMIC), in which the transceiver device for the radar signal is integrated on a chip together with control units and further circuit parts necessary to operate the radar sensor. Because of manifold setting possibilities and of operating states to be monitored for safety reasons, it is hardly possible to implement the setting of operating parameters to control the sensor and the readout of operating states in analog form via separate terminals (pins) of the integrated radar sensor component. It is therefore advisable for the control and for the readout to also integrate an interface unit in the radar sensor component and to exchange control and state information via a digital interface. A serial interface is particularly capable of keeping the number of pins on the housing of the radar sensor component as small as possible. For example, the serial peripheral interface bus (SPI bus), which allows a bidirectional data exchange using three or four pins, has a suitable interface.
Digital signals, e.g., as a clock signal and as a data signal, having a frequency in the range of several hundred kilohertz (kHz) to several megahertz (MHz), are typically used to operate the digital serial interface. Because of the integrated configuration of the radar sensor, however, crosstalk of the digital signals into the transceiver device of the radar sensor is unavoidable. This results in the occurrence of interfering side lines or side bands in the frequency spectrum of the emitted radar signal during operation of the digital interface. Since the side bands are outside the frequency band permissible for the radar transmitter, permitted radiation limiting values may be exceeded by the side bands.